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Archive for February, 2011

As ISP servers are having to be made harder and harder to reject spam, more and more people are finding that badly configured systems start to have their mail rejected.

A very common fault is failing to set the name that a Microsoft Exchange Server uses when it initiates an SMTP conversation across the internet. The HELO parameter of a conversation used to be logged and ignored but these days it’s very common indeed for servers to check the parameter makes sense. One of the things they will do is check that the name can be looked up on DNS.

If you don’t tell your Exchange Server what name to use, it’ll make one up using it’s own name and your local network name. Commonly, this will be something like mailserver.fredbloggs.local . Microsoft have long recommended using a .local domain name for internal networks and this is one of the results. Sadly, a .local name means nothing to the rest of the internet (that’s why you use it) but this means you have to provide the “Glue” by which external (i.e. anyone outside your network) servers use to confirm you are you.

It’s a simple configuration change you should only ever need to make once, and it won’t affect how your server behaves within your local network. It just changes how your server introduces itself to other people’s servers when it connects to them to try to send emails.

NOTE that you should try to ensure that the “reverseDNS” for the public IP address of your mail server matches this too. At the moment its common to check that there IS an IP address for the name given, in future it will be more common to check that this IP address is the SAME as the IP address from which the connection is originating. SO if you can’t get your ISP to change your ReverseDNS entry to match mail.fredbloggs.com, then it may be necessary to find what they DO give as your ReverseDNS (e.g. adsluser123.isp.com) and make your FQDN match that.